If your soups taste extremely basic, the cheapest and easiest way to level them up (without buying a bunch of intimidating spices) is to brown your butter before you begin. The intense flavor of that butter will stretch the mileage of your onions, garlic, and any other flavors you’re adding to the pot.
This soup is mushroom, but if you combine brown butter and parmesan, any and every soup you make will be noticeably better. Just keep a close eye on it and don’t let the butter burn. It’s ready as soon as it starts to smell nutty and delicious.